1. FIELD OF THE INVENTION
This invention relates to a novel process for preparing 4-oxopentadecanedionic acid, useful as an intermediate for musk perfume compounds such as cyclopentadecanone VI and cyclopentadecanolide VI-L. These musk perfume compounds have a similar macrocyclic structure as natural musk perfume compounds.
2. DESCRIPTION OF PRIOR ARTS
There have been known various processes for obtaining a macrocyclic musk perfume compound. But they have disadvantages: Some of them give only a low yield: some employ poisonous heavy metal compounds such as manganese and lead; some employ Grignard agents which will cause safety troubles; some employ starting materials which are not available with ease. Among conventional processes, there is an interesting process in which cyclopentadecanone VI is prepared by acyloin condensation and reduction of dimethyl pentadecanedioate V (Yonetani et al: The KORYO, No. 48, p 22-25, 1958). Dimethyl pentadecanedioate V can be obtained by reducing 4-oxopentadecanedioic acid IV, which is the object of this invention and will be hereinafter referred to as ketodicarboxylic acid, with hydrazine hydrate in the presence of potassium hydroxide and then esterifying the resulting product. The compound VI is also obtainable by acyloin condensation and reduction of the compound IV after the protection of its carbonyl group by forming a ketal. ##STR2##
As to a process for preparing 4-oxopentadecanedioic acid by oxidation and cleavage of the ethylenic unsaturated bond of a cyclic compound, Japanese patent publication 21690/70 discloses oxidation of bicycloketone VII. Bicycloketone is prepared from cyclododecanone VIII through three steps with the total yield of about 63 percent (Japanese patent publication 4341/69). Since 4-oxopentadecanedioic acid is obtained by ozone oxidation of bicycloketone VII with a yield of 63 to 77 percent, the yield of 4-oxopentadecanedioic acid from cyclododecanone VIII will be 40 to 49 percent. ##STR3##
As to the first step in which cyclododecanone VIII is converted to bicycloketone VII, there is known a process for preparing an unsaturated bicarboxylic acid half ester by the Stobbe condensation reaction between cyclododecanone and succinic acid diester such as diethyl succinate. As disclosed in Japanese patent publication 4341/69, the unsaturated half ester is obtained with two chemical structures, namely, the alkylidene type III and the alkenyl type II. The proportion of these two isomers is referred to in Biemann et al: J. Am. Chem. Soc., 79, 5558 (1957), in which the product of the alkylidene type was identified with UV spectrum. When the product, diethyl succinate is employed, the product III will be the main product U.S. Pat. No. 3,778,483 discloses a process for preparing the product of the alkenyl type from cyclododecanone and dimethyl or diethyl succinate, referred to as method B. But according to that patent, it is merely taught that bicycloketone is prepared by treatment with polyphosphoric acid, but it is not taught in detail that that of alkenyl type is selectively obtained.